Device for electro-optically ascertaining holes in moving webs

ABSTRACT

A device for electro-optically ascertaining holes in moving webs of paper and the like, in which on opposite sides of the path over which the web is moved there are respectively arranged a light source and light sensitive means the inlet signals of which are conveyed to amplifiers. The light source includes a threadshaped filament extending transverse to the direction of movement of the web to be checked, and the light sensitive means are arranged in pairs with the elements of each pair respectively arranged in two common rows located one behind the other and substantially parallel to the longitudinal direction of the filament, the elements of the light sensitive means of each pair being electrically opposed to each other in such a way that light simultaneously hitting both elements of one and the same pair of light sensitive means will not initiate a signal.

United States Patent Lippke, deceased DEVICEFOR ELECTRO-OPTICALLY ASCERTAINING HOLES IN MOVING WEBS Inventor: Paul R. Lippke, deceased, late of Beringstr. 41, 545 Neuwied 1, Germany by Rudolf Hiemke,

executor Filed: Nov. 20, 1972 Appl. No.: 308,013

Foreign Application Priority Data Nov. l8,l97l Germany ..2157247 References Cited UNITED STATES PATENTS Preston US. Cl. 250/561, 356/200, 356/239, Int. Cl G011] 21/16, G01n 21/32, 250/572 Field of Search.. 250/219 DF; 356/239, 200

[ May 21, 1974.

Primary Examiner-Archie R. Borchelt n Assistant Examiner-T. N. Grigsby Attorney, Agent, or Firm-Walter Becker ABSTRACT mon rows located one behind the other and substantially parallel to the longitudinal direction of the filament, the elements of the light sensitive means of each pair being electrically opposed to each otherin such a way that light simultaneously hitting both elements of one and the same pair of light sensitive means will not initiate a signal. I r

4 Claims, 4 Dra wing Figures PATENTEDHAYZ? 1814 3812.348

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DEVICE FOR ELECTRO-OPTICALLY ASCERTAINING HOLES IN MOVING WEBS The present invention relates to a device for electrooptically ascertaining holes in moving webs of paper and the like, in which at one side of the web there is provided an illuminating device whereas on the other side there are provided light sensitive elements the emanated signals of which are conveyed to amplifiers.

A device of this general character is described, for instance, in German Auslegeschrift No. 1,203,017.

An important disadvantage of the heretofore known device consists in that the light source as well as the photoelectric cells have to be arranged closely below or above the web if a hole in the web is to initiate a signal for indicating a flaw in the web. If the photoelectric cells are spaced from the web at a greater distance, they will no longer be able to emanate a sufficiently strong signal to indicate a flaw because the light of luminous substance lamps with relatively large illuminating surfaces emanates with a correspondingly low illu- 'minating density so that the illuminating strength in the plane of the light sensitive elements will change only immaterially or to an insufficient degree. This is true if the diameter of a hole-is approximately 1 mm as is frequently the case with holes in paper webs.

In view of the necessary arrangement of the light sensitive elements of photoelectric cells closely below or above the web, there exists, on the one hand, the danger of damage to the sensitive testing or checking device in case the web should tear because in such an instance a considerable quantity of material will accumulate in front of the checking device in a short time. On the other hand, it is difficult, after a break in the web has occurred, again to pass the web through the relatively narrow gap between the illuminating device and the photoelectric cells.

The above mentioned difficulties and disadvantages have been overcome by other heretofore known testing or checking devices of the type involved by employing ultraviolet radiation emanating radiation sources together with correspondingly sensitized detectors instead of ordinary incandescent lamps with their visible light. With such device, the detectors can be arranged at a considerably greater distance from the web than is the case with the photoelectric cells of the first mentioned device. The reason for this consists in that the employed ultraviolet radiation of predetermined wave length is nearly completely absorbed by the paper so that a hole in the web will, in spite of the great distance between web and detectors, permit such a great quantity of ultraviolet rays to reach the detectors as is the case when no holes are present in the web with the result that the detectors will initiate the indication of a flaw. In view of the high degree of absorption of ultraviolet radiation by the paper, it is immaterial that the ultraviolet radiation passing through the hole is emanated by a relatively large surfaced radiatingsystem or emitter. An important disadvantage of this known device is, however, seen in the costs for the device itself and for operating such device.

With such a device, the illuminating system together with the necessary special current supply causes high costs. In addition thereto, the employed extremely sensitive photo multipliers together with the necessary filters which correspond to the ultraviolet radiation and which are intended to eliminate the influence of outside light, are expensive. Moreover, operators remaining for a longer period of time within the range of the checking device may suffer eye damage.

It is, therefore, an object of the present invention to provide a device of the type involved which will have relatively simple elements only and which will be safe in operation while the distance between the illuminating device and the light sensitive elements can be made relatively great. v

This object and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawing, in which:

FIG. 1 is a side view and partially a section of a device according to the invention.

FIG. 2 shows the arrangement of the light sensitiv elements on a support;

FIG. 3 illustrates a front view of preferred incandescent lamps for the illuminating device.

FIG. 4 illustrates an electric circuit for compensating for the influence of the light which continuously passes from the surrounding area onto the light sensitive elements.

The device for electro-optically ascertaining holes in moving webs of paperand the like according to the invention is characterized primarily in that an illuminating device is provided with a thread-Iike light source arranged transverse to the direction of movement of the web, and is furthermore characterized in that the light sensitive elements are arranged in pairs while the elements forming the pairsare located in one or the other of two rows which are located one behind the other in the direction of movement of the web and are parallel to the longitudinal extensionof the light source while being located in a plane parallel to the plane of the web. The device according to the invention is also characterized in that the elements of each pair are electrically arranged in series-opposed manner so that light which simultaneously hits two elements of one or more pairs will not initiate asignal.

When a hole shows up in the web, the thread-shaped light source is in conformity with the function of a pinhole camera portrayed in the plane of the light sensitive elements. By taking advantage of this effect, it is possible to arrange the light sensitive elements at a greater distance from the web and nevertheless to obtain a signal which is sufficient for indicating a flaw. For instance, a device according to the present invention has yielded satisfactoryv checking results if the light source or the light source and the light sensitive elements respectively were arranged at a distance of approximately 30 cm from the web. The imageof the thread-shaped light source in the plane of the light sensitive elements is for holes nonnally occurring in paper webs so sharp and bright combined with a corresponding increase in the illuminating strength at this point that the signal emanated when a hole is present is sufficient to indicate a flaw. This effect, which is taken advantage of in connection with the invention, would not occur if instead of a thread-like light source, for instance, incandescent lamps with frosted glass bulbs were employed or corresponding luminous substance lamps were used. .These,

iamps, on the one hand, have too large a light emanating surface so that they cannot furnish a sufi'tciently'effective signal when taking advantage of the just described effect. On the other hand, they have too low an illuminating density.

For instance, incandescent lamps with frosted glass bulbs have an illuminating density of 50 cdlcm whereas the thread-shaped light sources employed with 'the device according to the invention have a light densityof 2,000 cdlcm Tubes with luminous substance have a still lower light density than incandescent lamps with frosted glass'bulbs.

With the device according to the present invention, by means of which substantially only holes are to be ascertained, it will be appreciated that, in view of the relatively great distance of the light sensitive elements from the web, there willadditionally be realized the advantage that the cloudiness or slight irregularities of a paper web will, due to the considerable straying of the light, have not only no or only an immaterial influence on the formation of a signal.

It is furthermore suggested that as light source there are provided one or more tube-shaped incandescent lamps with clear glass bulbs and with thin incandescent filaments. in this way, the illuminating device can be produced in a simple manner. However, it is also possible in stead of the suggested incandescent lamps to build up the illiminating device with other incandescent lamps or light emanating devices in which instance care has to be taken to the effect that the area of the light exit is thread-shaped and that 'a sufficiently high light density is obtained at the light exit.

it is also possible by suitable electric arrangements, as for instance electric bias for the elements following the amplifiers to compensate for the light which continuously impacts upon the light sensitive elements arranged in a row, namely for the light which emanates from the paper web and which passes from the surrounding area onto the elements. Such steps will, however, be insufticient when the illuminating conditions in the plane of the light sensitive elements change during operation. A change of the general illuminating strength is, however, to be expected because the light sensitive elements are exposed to the possibly varying influences of the light from the light sources in the vicinity of the device and because the medium light transparency of the webs to be checked may change.

In order to avoid the just described difficulties, light sensitive elements according to the invention are arranged in pairs and with regard to each pair are electrically arranged in a series-opposed manner. In this way only such light influences can initiate'a signal which hit the two elements of one or more pairs in a non-uniform manner. This is the case when portraying the threadshaped light source in the plane of the elements in case there is a hole in the web. In such an instance first one and subsequently the other light sensitive element of each pair receives a higher illuminating strength.

* Referring now to the drawings in detail, the reference numeral 1 designates a web which, for instance, is

moved in the indicated direction over two rollers 2 and 3. At one side of the web 1 there is located an illuminating device 4 which comprises primarily a housing 5 with incandescent lamps 6. On the other side of the web there are located light sensitive elements 10, 11 arranged on a support 13. The incandescent lamps 6 have a preferably non-coiled thin filament 7 which forms the light source. The filaments 7 of the incandescent lamps 6 arranged adjacent to each other in the housing 5 portray a nearly uninterrupted thread-shaped light source which extends transverse to the direction of movement of the web and is located parallel or nearly parallel to the rows 8 and 9 of the light sensitive elements 10, 11. The thickness of the filaments 7 is of a magnitude of 1/ l0 mm so that when a hole occurs in the web 1, a relatively sharp image of the filament or filaments 7 is obtained in the plane of the light sensitive elements 10 and 11 without any optical auxiliary means. Such image of a filament is illustrated in FIG. 2 and designated with the reference numeral 12. The image 12 extends with sufficient .illuminating strength in the plane of the elements over a plurality of elements 10, ll of a row so that the suggested device according to the invention furnishes the further advantage that only relatively few light sensitive elements are needed for checking the entire width of a web because the elements of each row may be arranged at a relatively great distance from each other on a support 13.

It is also possible to replace the illustrated incandescent lamps by a corresponding plurality of incandescent lamps with point-shaped light sources, if such incandescent lamps are arranged closely adjacentto each other. Aside from the difficulty of producing for this purpose sufficiently point-shaped light sources, and aside from the employment of a greater number of elements, it would additionally be necessary to arrange the light sensitive elements of a row closer adjacent to each other so that also more of these elements would be needed.

The incandescent lamps 6 are provided with glass bulbs 14 which, for all practical purposes, do not affect the optical function The filament 7 of' an incandescent lamp 6 is connected with the two contacts 15 and 16 for the supply of current. The filament 7 is held in its predetermined position by a supporting coil 17.

In view of the movement of the web 1, an image 12 will first pass over the light sensitive elements 11 of row 9 and subsequently will pass over or scan the elements 10 of row 8. The outlets of the light sensitive elements 10 and 11, which elements are arranged in pairs 22 on the support 13, are connected to one or the other inlet of differential amplifiers 18. Additional devices 19 for indicating flaws are connected to the outlets of the amplifiers 18. in order to improve the effect of the images 12 and to compensate for changes of the light impacting from the surrounding area upon the light sensitive elements 10 and 11, a suitable bias is conveyed to the inlet of the differential amplifiers 18. This is done by a voltage divider 20, 21. p

It is furthermore advantageous for purposes of eliminating interfering influences, for instance due to shade formation by articles in the plane of the elements, to

arrange the elements in such a way within the framework of a paper making machine or the like that the surrounding daylight or the light of the light; source in the vicinity will not or will not directly pass onto the elements.

A particular advantage of the device according to the invention consists in that it operates without any auxiliary optical means.

It is, of course, to be understood that the present invention is, by no means, limited to the particular showing in the drawing but also comprises any modifications within the scope of the appended claims.

What I claim is:

1. A device for electro-optically ascertaining holes in a moving web, especially web of paper, which includes: a source of illumination comprising a thread-shaped light source, light sensitive means adapted to initiate a signal, said light sensitive means being arranged in pairs one behind the other so that the two light sensitive means of all of said pairs are respectively arranged in two common seperate rows substantially parallel to each other and to the longitudinal extension of said thread-shaped light source, said light sensitive means also having outlets for releasing signals, said source of illumination and said light sensitive means being arranged one above the other in spaced relationship to each other, and conveying meansfor conveying a web between and in spaced relationship to said source of illumination and said light sensitive means, said threadshaped light source having its direction of length arranged transverse to the conveying direction of said conveying means, and the light sensitive means of each of said pairs of light sensitive means electrically oppos- 6 ing each other so that light simultaneously hitting both light sensitive means of one and more of said pairs will not initiate a signal.

2. A device according to claim 1, in which the light source comprises at least one tubular incandescent lamp with a thin filament in aclear glass bulb.

3. A device according to claim 1, which includes a voltage divider, and differential amplifier means having inlets respectively electrically connected to the outlets of the pairs of said light sensitive means through said voltage divider for compensating for the influence of undesired light hitting said light sensitive means.

4. A device according to claim 1, in'which said light sensitive means are protected against the influence of undesired surrounding light from surrounding foreign light sources by shields. 

1. A device for electro-optically ascertaining holes in a moving web, especially web of paper, which includes: a source of illumination comprising a thread-shaped light source, light sensitive means adapted to initiate a signal, said light sensitive means being arranged in pairs one behind the other so that the two light sensitive means of all of said pairs are respectively arranged in two common seperate rows substantially parallel to each other and to the longitudinal extension of said thread-shaped light source, said light sensitive means also having outlets for releasing signals, said source of illumination and said light sensitive means being arranged one above the other in spaced relationship to each other, and conveying means for conveying a web between and in spaced relationship to said source of illumination and said light sensitive means, said threadshaped light source having Its direction of length arranged transverse to the conveying direction of said conveying means, and the light sensitive means of each of said pairs of light sensitive means electrically opposing each other so that light simultaneously hitting both light sensitive means of one and more of said pairs will not initiate a signal.
 2. A device according to claim 1, in which the light source comprises at least one tubular incandescent lamp with a thin filament in a clear glass bulb.
 3. A device according to claim 1, which includes a voltage divider, and differential amplifier means having inlets respectively electrically connected to the outlets of the pairs of said light sensitive means through said voltage divider for compensating for the influence of undesired light hitting said light sensitive means.
 4. A device according to claim 1, in which said light sensitive means are protected against the influence of undesired surrounding light from surrounding foreign light sources by shields. 